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Example code using a timer with the BeagleBone Black's PRU microcontroller. This code generates 5 pulses with 100ns width.
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/* | |
* Demonstration of the BeagleBone's PRU, using a timer. | |
* Ken Shirriff, http://righto.com | |
*/ | |
#include <stdint.h> | |
#define DELAY_NS 100 // Use 500000000 for 0.5 second delay | |
#define WRITE_PIN 15 /* P8_11, Ethernet output data, pr1_PRU0_pru_r30_15 */ | |
// PRU Interrupt control registers | |
#define PRU_INTC 0x00020000 // Start of PRU INTC registers TRM 4.3.1.2 | |
#define PRU_INTC_GER ((volatile uint32_t *)(PRU_INTC + 0x10)) // Global Interrupt Enable, TRM 4.5.3.3 | |
#define PRU_INTC_SICR ((volatile uint32_t *)(PRU_INTC + 0x24)) // Interrupt, TRM 4.5.3.6 | |
#define PRU_INTC_GPIR ((volatile uint32_t *)(PRU_INTC + 0x80)) // Interrupt, TRM 4.5.3.11 | |
// PRU ECAP control registers (i.e. PWM used as a timer) | |
#define ECAP 0x00030000 // ECAP0 offset, TRM 4.3.1.2 | |
// Using APWM mode (TRM 15.3.2.1) to get timer (TRM 15.3.3.5.1) | |
#define ECAP_TSCTR ((volatile uint32_t *)(ECAP + 0x00)) // 32-bit counter register, TRM 15.3.4.1.1 | |
#define ECAP_APRD ((volatile uint32_t *)(ECAP + 0x10)) // Period shadow, TRM 15.3.4.1.5, aka CAP3 | |
#define ECAP_ECCTL2 ((volatile uint32_t *)(ECAP + 0x2a)) // Control 2, TRM 15.3.4.1.8 | |
#define ECAP_ECEINT ((volatile uint16_t *)(ECAP + 0x2c)) // Enable interrupt, TRM 15.3.4.1.9 | |
#define ECAP_ECCLR ((volatile uint16_t *)(ECAP + 0x30)) // Clear flags, TRM 15.3.4.1.11 | |
// R30 is the GPIO register | |
// R31 is the interrupt register | |
volatile register unsigned int __R31, __R30; | |
// Forward definitions | |
void init_pwm(); | |
void wait_for_pwm_timer(); | |
void main() { | |
init_pwm(); | |
int i; | |
for (i = 0; i < 5; i++) { | |
wait_for_pwm_timer(); | |
__R30 = 1 << WRITE_PIN; | |
wait_for_pwm_timer(); | |
__R30 = 0; | |
} | |
__R31 = 35; // Interrupt to host | |
__halt(); | |
} | |
// Initializes the PWM timer, used to control output transitions. | |
// Every DELAY_NS nanoseconds, interrupt 15 will fire | |
inline void init_pwm() { | |
*PRU_INTC_GER = 1; // Enable global interrupts | |
*ECAP_APRD = DELAY_NS / 5 - 1; // Set the period in cycles of 5 ns | |
*ECAP_ECCTL2 = (1<<9) /* APWM */ | (1<<4) /* counting */; | |
*ECAP_TSCTR = 0; // Clear counter | |
*ECAP_ECEINT = 0x80; // Enable compare equal interrupt | |
*ECAP_ECCLR = 0xff; // Clear interrupt flags | |
} | |
// Wait for the PWM timer to fire. | |
// see TRM 15.2.4.26 | |
inline void wait_for_pwm_timer() { | |
while (!(__R31 & (1 << 30))) {} // Wait for timer compare interrupt | |
*PRU_INTC_SICR = 15; // Clear interrupt | |
*ECAP_ECCLR = 0xff; // Clear interrupt flags | |
} |
Hello, how can I compile and run this snippet on my Beaglebone Black? I'm sorry for posing such a novice question. I've tried searching your blog, but couldn't find any solutions. Thanks
I'm not the author but you essentially download http://www.ti.com/tool/PRU-CGT and use a makefile from one of the PRU example such as those examples in the sdk http://www.ti.com/tool/PROCESSOR-SDK-AM335X
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Hello, how can I compile and run this snippet on my Beaglebone Black? I'm sorry for posing such a novice question. I've tried searching your blog, but couldn't find any solutions. Thanks